The present invention relates to a plasma address electrooptical device that controls the display of electrooptical elements by use of plasma discharge.
Similar to the plasma display panel (PDP), a plasma address electrooptical device (plasma address liquid crystal display; PALC) is utilized as the major component of a large-sized flat panel display device.
An example of a plasma address electrooptical device utilizing a discharge plasma switch to drive a liquid crystal cell will now be explained.
FIG. 5 is a partial perspective view showing the plasma address electrooptical device according to the prior art. Actually, hundreds of liquid crystal drive electrodes and discharge cells are arranged in the device, but the drawing shows only a portion of them as an example.
As shown in FIG. 5, the plasma address electrooptical device 100 comprises liquid crystal cells 101 and plasma cells 102 mounted on a common dielectric layer 103. The plasma cell 102 comprises a plurality of discharge cells 105 formed between a dielectric layer 103 and a lower substrate 104. A plurality of grooves are formed to the surface of the lower substrate 104 facing the dielectric layer 103, and each discharge cell 105 is defined by a groove being sealed by the discharge layer 103. A gas capable of being ionized by discharge is sealed inside each discharge cell 105, and a pair of plasma electrodes 106 and 107 is formed to the bottom of each cell. When voltage is imposed to the discharge cell 105 utilizing one of the pair of plasma electrodes 106 and 107 as anode and the other as cathode, the gas sealed inside the discharge cell 105 is ionized, and discharge plasma is generated.
On the other hand, the liquid crystal cell 101 comprises a liquid crystal layer 109 mounted between the upper substrate 108 and the dielectric layer 103. A plurality of liquid crystal drive electrodes 110 arranged parallel to one another are formed on the surface of the upper substrate 108 facing the liquid crystal layer 109. The liquid crystal drive electrodes 110 are arranged so as to cross the grooves (discharge cells 105) formed on the lower substrate 104, and individual pixels are each defined on the crossed areas.
The displaying method according to this plasma address electrooptical device is explained with reference to FIG. 6.
As shown in FIG. 6(a), by discharging one discharge cell (not shown) corresponding to a selected data sequence, charged particles are stored to the charged particle storage portion 111 formed on the surface of the dielectric layer 103 facing the discharge cell, so that the potentials of the stored portion are 0 V. By simultaneously imposing voltage data corresponding to the selected data sequence to the plurality of liquid crystal drive electrodes 110, the discharge cells function as switching elements for the liquid crystal layer 109. Therefore, the amount of electric charge corresponding to the data sequence is stored to the charged particle storage portion 111 on the surface of the dielectric layer 103 facing the discharge cell, and the electric field corresponding to one data sequence is applied to the liquid crystal cell, the status of which is maintained. This procedure is repeated for the number of discharge cells, and the voltage imposed to each liquid crystal drive electrode 110 is maintained until the same discharge cell is discharged for the next frame. Thereafter, until the data for the next frame is transmitted (FIG. 6(d)), as shown in FIG. 6(b) and FIG. 6(c), data voltage corresponding to other discharge cell portions is imposed thereto, with the liquid crystal drive voltage being reversed. Every time the display is changed, the voltage imposed to the liquid crystal drive electrode 110 is reversed between positive and negative polarities. According to the example shown in FIG. 6, the device is driven so that voltage is imposed only to the pixel corresponding to red (R).
According to such plasma address electrooptical device, display leakage (hereinafter called xe2x80x9ccross talkxe2x80x9d) tends to occur to adjacent pixels in the display sequence corresponding to the same discharge cell. In other words, although liquid crystal drive voltage is imposed to the liquid crystal drive electrode that corresponds to only one pixel constituting one data point, as a result, cross talk is observed on the display. When cross talk occurs, the display grade of the device reduces greatly. For example, if colored images are to be displayed, one pixel, in other words, one liquid crystal drive electrode is allocated to one of the colors, R (red), G (green) or B (blue), and a colored filter is mounted on the pixel. If cross talk occurs when only red is to be displayed on the screen, as shown in the example of FIG. 6 (when electric field is applied to only the pixel corresponding to R, and no electric field is applied to pixels corresponding to adjacent pixels G and B), display leakage is observed to portions of adjacent pixels G and B. As a result, clear red color cannot be displayed on the screen, and the color purity is reduced.
As shown in FIG. 6, 30 V is the amount of voltage needed to be imposed to the liquid crystal drive electrode in order to apply an electric voltage of 1 V/xcexcm to the inner area of the liquid crystal layer. In other words, since the sum thickness of the liquid crystal layer and the dielectric layer is 30 xcexcm, when 30 V is imposed to the liquid crystal drive electrode and charged particles are stored to the charged particle storage portion on the surface of the dielectric layer facing the discharge cell so that the electric potential thereof becomes 0 V, an electric field of 1 V/xcexcm is applied to the interior of the liquid crystal layer.
The amount of leakage of an image to the adjacent pixels is hereinafter called the cross talk width. That is, as shown in FIG. 7, a center line shown by a chain single-dashed line is supposed to exist between pixels. The cross talk width refers to the length from the center line to the area of the adjoining pixel that is influenced by the information of a pixel. The intensity of display at the cross talk portion is hereinafter called the cross talk intensity. In other words, when a display of a pixel is leaked to adjacent pixels, the similarity of the display of the pixel and the display of the display leakage area is called the cross talk intensity. Actually, the cross talk intensity is expressed as strong when the display of a pixel is black and the display leakage area also displays black, and expressed as weak when the display of a pixel is black and the display leakage area displays a lighter color, such as gray.
Until now, cross talk was considered to be caused by the electric field that has been generated by the voltage imposed to the liquid crystal drive electrode and which protruded (leak out) beyond the intended electrode region. However, the amount of leakage of the electric field or the mechanism of the leakage was still mainly unknown, since it involved the structure of the device or the behavior of the discharged particles being stored.
Examples of the methods for restraining the cross talk proposed heretofore are explained in the following.
Japanese Patent Application Laid-Open Publication No. 8-123360 discloses a method for restraining cross talk caused by the thickness of the dielectric layer, by providing in advance a correction arithmetic process by a correction circuit to the data sequence signal that is to be applied to the liquid crystal drive electrode.
Moreover, Japanese Patent Application Laid-Open Publication No. 10-148820 discloses a method for restraining cross talk by arranging electrode groups in parallel with the liquid crystal drive electrodes on the surface of the dielectric layer facing the discharge cell. By arranging electrode groups, the ununiformity of charge density vanishes, and the fringe electrical field of adjacent liquid crystal drive electrodes is reduced, which leads to restrained cross talk.
However, the methods disclosed in the above-mentioned publications had the following problems.
The method disclosed in Japanese Patent Application Laid-Open No. 8-123360 utilizes a drive circuit for restraining cross talk, and therefore, a large-scale integrated circuit device must be additionally provided to the conventional plasma address electrooptical device. Accordingly, it was substantially difficult to perform a correction computing process corresponding to various images.
Moreover, the method disclosed in Japanese Patent Application Laid-Open No. 10-148820 includes electrodes arranged on the surface of the dielectric layer facing the discharge cell. Therefore, it was necessary to locate all the liquid crystal electrodes, the parallel electrode group and the discharge cells to their respective positions, and it was difficult to position all these elements.
The present invention aims at solving the above problems of the prior art. The object of the invention is to provide a plasma address electrooptical device that enables to restrain cross talk by a relatively simple yet effective method.
In order to solve the above-mentioned problems, the present invention provides a plasma address electrooptical device comprising a plurality of liquid crystal drive electrodes mounted on a first substrate, and a plurality of discharge cells formed on a second substrate, the liquid crystal drive electrodes being positioned so as to oppose to the discharge cells through at least a liquid crystal layer and a dielectric layer; wherein the distance between a first liquid crystal drive electrode and a second liquid crystal drive electrode adjacent the first liquid crystal drive electrode is either equal to or greater than the distance between the surface of the first liquid crystal drive electrode and the surface of the dielectric layer closer to the second substrate.
Moreover, it is preferable that the present device further comprises an auxiliary electrode being insulated from the liquid crystal drive electrodes which is each arranged between said first and second liquid crystal drive electrodes.
The plasma address electrooptical device according to the present invention comprises a plurality of liquid crystal drive electrodes mounted on a first substrate, and a plurality of discharge cells formed on a second substrate, the liquid crystal drive electrodes being positioned so as to oppose to said discharge cells through at least a liquid crystal layer and a dielectric layer; wherein auxiliary electrodes being insulated from said liquid crystal drive electrodes are each arranged between adjacent liquid crystal drive electrodes.
The plasma address electrooptical device according to the present invention preferably comprises a means for controlling the electric potential of the auxiliary electrodes.
The electric potential of the auxiliary electrodes is preferably set to 0 V according to the plasma address electrooptical device of the present invention.
The operation according to the present invention will now be explained.
According to the invention, the distance between the first liquid crystal drive electrode and the adjacent second liquid crystal drive electrode is set to be equal to or greater than the distance between the first liquid crystal drive electrode surface and the surface of the dielectric layer facing the second substrate, and thereby, cross talk is restrained. In other words, the distance between the first liquid crystal drive electrode to which voltage is imposed and the charged particle storage portion formed on the surface of the dielectric layer facing the discharge cell is either equal to or greater than the distance between adjacent liquid crystal drive electrodes. Therefore, the electric line of force generated from the first liquid crystal drive electrode to which voltage is imposed extends toward the charged particle storage portion on the surface of the dielectric layer facing the discharge cell. This weakens the electric field generated to adjacent pixel portions, and only gray color appears on the adjacent pixel areas. In other words, the cross talk intensity is reduced.
Even further, a novel effect could be expected by widening the distance between the liquid crystal drive electrodes. That is, when the distance between the liquid crystal drive electrodes widen, the width of the liquid crystal drive electrode reduces at the same time. The example of a 42-inch panel is explained. When considering the so-called HD (high density) type display, the repeating distance of the liquid crystal drive electrodes is approximately 180 xcexcm. Accordingly, when the distance between the liquid crystal drive electrodes is set to 20 xcexcm, the width of each liquid crystal drive electrode is 160 xcexcm. Therefore, if the distance between the liquid crystal drive electrodes is set to 40 xcexcm, the width of each liquid crystal drive electrode is reduced down by more than 10% to 140 xcexcm. When the width of the liquid crystal drive electrode is reduced, the area of the charge particle storage portion formed on the surface of the dielectric layer facing the discharge cell is also reduced, and the amount of charged particles to be stored thereto can be reduced. Accordingly, the voltage needed to drive the liquid crystal in order to realize the same display status (luminance) may be reduced. When the liquid crystal drive voltage is reduced, the cross talk width is also reduced. In other words, the cross talk width is even further reduced by widening the distance between the liquid crystal drive electrodes.
As for the electric field applied to the liquid crystal layer, the thickness of the layer other than the liquid crystal layer and the dielectric layer may become a problem. For example, an ultraviolet block film (for example, a film mainly formed of titanium oxide) having a thickness of 2 to 3 xcexcm may be inserted between the liquid crystal layer and the dielectric layer, in order to prevent ultraviolet from being radiated to the liquid crystal layer from the plasma unit. In this case, the thickness of the ultraviolet block film is added to the thickness of the liquid crystal layer and the dielectric layer, and electric field is applied to these three layers. That is, when ultraviolet block film exists within the device, the distance between the liquid crystal drive electrodes should be greater than the sum thickness of the three layers (the liquid crystal layer, the dielectric layer and the ultraviolet block layer), in order to reduce the cross talk intensity.
Moreover, according to the present invention, cross talk may be restrained by providing auxiliary electrodes insulated from liquid crystal drive electrodes to the area between first and second liquid crystal drive electrodes.
That is, when an auxiliary electrode exists between the first and second liquid crystal drive electrodes, the electric line of force generated from the charged particle storage portion on the surface of the dielectric layer facing the discharge cell is extended toward the nearest auxiliary electrode at first, before reaching the second liquid crystal drive electrode placed adjacent to the first electrode. The electric line of force will be converged to the edge of the second liquid crystal drive electrode, and the line of force is restrained from widening, which leads to reduced cross talk width.
Moreover, by providing all the above-explained features to one electrooptical device, the intensity and the width of the cross talk can be reduced simultaneously.
Moreover, according to the present invention, the cross talk may be further restrained by controlling the electric potential of the auxiliary electrodes.
For example, by applying a means to connect the auxiliary electrodes and a 0 V position through a connection cable, the auxiliary electrodes may be constantly controlled to 0 V. Thereby, the auxiliary electrodes and the adjacent second liquid crystal drive electrodes will have the same electric potentials, and therefore, no electric line of force will exist between the auxiliary electrodes and the second liquid crystal drive electrodes. Accordingly, the electric field above the adjacent second liquid crystal drive electrode is greatly reduced, since the only electric line of force existing on the second electrode is the one directly generated from the charged particle storage portion on the surface of the dielectric layer facing the discharge cell. Cross talk is thereby reduced even further.